Light-reflective anisotropic conductive adhesive agent, and light emitting device

ABSTRACT

A light-reflective anisotropic conductive adhesive and light-emitting device capable of maintaining luminous efficiency of a light-emitting element and preventing the occurrence of a crack to obtain conduction reliability are provided. The light-reflective anisotropic conductive adhesive contains a thermosetting resin composite, conductive particles, and a light-reflective acicular insulating particles. These light-reflective acicular insulating particles are inorganic particles of at least one type selected from the group including titanium oxide, zinc oxide, and titanate.

FIELD OF THE INVENTION

This invention relates to a light-reflective anisotropic conductiveadhesive to be used for anisotropic conductive connection of alight-emitting element onto a wiring board, and a light-emitting devicehaving a light-emitting element mounted on a wiring board by using thislight-reflective anisotropic conductive adhesive.

The present application claims priority rights to JP Patent Application2010-092672 filed in Japan on Apr. 13, 2010, which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

Conventionally, a light-emitting device using a light-emitting elementsuch as a light-emitting diode (LED) has been widely used. FIG. 3 toFIG. 5 each depict an example of structure of a light-emitting device ofan old type. In manufacture of the light-emitting device depicted inFIG. 3, an LED element 33 is bonded onto a substrate 31 with a die bondadhesive 32, and a p electrode 34 and an n electrode 35 on an uppersurface of the LED element 33 are wire-bonded to the substrate 31 withgold (Au) wires 37 by silver plating 36. With this, the LED element 33and the substrate 31 are electrically bonded together. Normally, thewhole LED element 33 is sealed with a resin such as a transparent moldresin (not shown). In some cases, exfoliation may occur at a connectingportion of any of the gold wires 37 due to a difference in coefficientof linear expansion between the resin, and the LED element 33 and thegold wires 37, and an electric connection defect may occur due to abreak of any of the gold wires 37.

In general, for this light-emitting device, it is desired to inhibit adecrease in reflectance of light emitted from the LED element andmaintain luminous efficiency (light extraction efficiency). In thelight-emitting device depicted in FIG. 3, metal electrodes are normallyused as the p electrode 34 and the n electrode 35 of the LED element 33.However, among light beams emitted from the LED element 33, a light beamhaving a wavelength of 400 nm to 500 nm emitted to an upper surface sideis absorbed into the gold electrodes and the gold wires, and a lightbeam emitted to a lower side is absorbed into the die bond adhesive 32.This light absorption decreases luminous efficiency (light extractionefficiency) of the LED element 33. Moreover, the adhesion process withthe die bond adhesive 32 is based on oven curing, therebydisadvantageously taking time for manufacture.

In the light-emitting device depicted in FIG. 4, a conductive paste 37typified by a silver paste is used. With this conductive paste 37, the pelectrode 34 and the n electrode 35 on the lower surface of the LEDelement 33 and the silver-plated portion 36 on the substrate 31 areelectrically bonded together. However, since the conductive paste 37 hasa weak adhesion force, reinforcement by a sealing resin 38 is required.Furthermore, light may be diffused or absorbed inside the conductivepaste 37, thereby decreasing luminous efficiency of the LED element 33.

Thus, for example, what is suggested is electrical bonding in which ananisotropic conductive adhesive (ACP) or an anisotropic conductiveadhesive film (ACP) is cured to connect and fix the LED element and thesubstrate together. For example, Patent Document 1 describes a method offlip-chip mounting the LED element. Also, for example, in thelight-emitting device depicted in FIG. 5, a commercially-availableanisotropic conductive adhesive 39 is used to electrically bond the pelectrode 34 and the n electrode 35 on the lower surface of the LEDelement 33 and the substrate 31 together by flip-chip mounting. In thisflip-chip mount technology, a bump 40 is formed on each of the pelectrode 34 and the n electrode 35.

In the technology of Patent Document 1, a light reflective layer such asa metallized layer is provided to the LED element so as to be insulatedfrom the p electrode and the n electrode. With this, a decrease inreflectance of light emitted from the LED element is inhibited tomaintain luminous efficiency. However, this technology of PatentDocument 1 has disadvantages such that the number of manufacturingprocesses of the light-emitting device is increased and cost isinevitably increased. On the other hand, in the light-emitting devicedepicted in FIG. 5, while a light reflective layer is not provided, Auor Ni to be used as conductive particles dispersed in an ACP binderappears brown or dark brown, and an imidazole-based latent curing agentnormally contained in the binder appears brown. For such reasons, theACP binder appears brown as a whole, thereby absorbing light. As aresult, luminous efficiency of the LED element 33 is decreased.

PRIOR-ART DOCUMENTS Patent Document

-   PTL 1: Japanese Patent Application Laid-Open No. 11-168235

SUMMARY OF THE INVENTION

Meanwhile, an epoxy resin is used as a binder resin in the ACP. In theACP using the epoxy resin, an increase in conduction resistance,exfoliation of an adhesion surface, a crack, and others occur due to aninternal stress based on a difference in coefficient of thermalexpansion with temperature changes with respect to a connectionsubstrate. For this reason, reliability may be decreased regardingcorresponding reflow of lead-free solder, resistance to thermal shock,resistance to a corrosion phenomenon of a vapor-deposited wiring whenused and stored in an atmosphere at high temperature and high humidity,and others.

The present invention was suggested in view of these conventionalcircumstances, and has an object in which, in a light-emitting devicewhere a light-emitting element such as an LED element is mounted on awiring board by using an anisotropic conductive adhesive by a flip-chipmethod to maintain luminous efficiency of the light-emitting elementwithout providing a light-reflective layer that may invite manufacturingcost to an LED element, the occurrence of a crack in the anisotropicconductive adhesive is prevented to obtain high conduction reliability.

The inventor of the present invention has found that the occurrence of acrack can be prevented by forming each light-reflective insulatingparticle to be added into the anisotropic conductive adhesive in anacicular shape.

That is, the present invention is directed to a light-reflectiveanisotropic conductive adhesive to be used for anisotropic conductiveconnection of a light-emitting element to a wiring board, the adhesivecontaining a thermosetting resin, conductive particles, andlight-reflective acicular insulating particles.

Also, in the present invention, a light-emitting element is mounted on awiring board by a flip-chip method via this light-reflective anisotropicconductive adhesive.

EFFECTS OF INVENTION

According to the light-reflective anisotropic conductive adhesive andlight-emitting device of the present invention, by addinglight-reflective acicular insulating particles into the anisotropicconductive adhesive, the occurrence of a crack in the light-reflectiveanisotropic conductive adhesive can be prevented to obtain highconduction reliability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a sectional view of a light-reflective conductive particle.

FIG. 1B is a sectional view of the light-reflective conductive particle.

FIG. 2 is a sectional view of a light-emitting device in a presentembodiment.

FIG. 3 is a sectional view of a conventional light-emitting device.

FIG. 4 is a sectional view of the conventional light-emitting device.

FIG. 5 is a sectional view of the conventional light-emitting device.

DETAILED DESCRIPTION OF THE INVENTION

An example of a specific embodiment (hereinafter referred to as a“present embodiment”) of the light-reflective anisotropic conductiveadhesive to which the present invention is applied is described belowwith reference to the drawings. The light-reflective anisotropicconductive adhesive in the present embodiment is an adhesive to be usedfor anisotropic conductive connection of an LED element, which is alight-emitting element, to a wiring board, and contains a thermosettingresin composite, conductive particles, and light-reflective acicularinsulating particles.

The light-reflective acicular insulating particles are characterized asbeing formed of an acicular shape with an aspect ratio having a valuewithin a predetermined range. When the thermosetting resin compositecontains globular particles, if elasticity is decreased with temperaturechanges, a crack may occur from an interface between the globularparticles and the thermosetting resin composite due to an internalstress of the thermosetting resin composite. As such, when a crackoccurs in the light-reflective anisotropic conductive adhesive,conductance reliability may be impaired. For this reason, thelight-reflective anisotropic conductive adhesive is required to haveexcellent toughness.

In the light-reflective anisotropic conductive adhesive in the presentinvention, acicular light-reflective insulating particles with an aspectratio within a predetermined range are added to a thermosetting resincomposite. In the thermosetting resin composite, acicularlight-reflective insulating particles each arranged in a randomdirection cause an internal stress of the thermosetting resin compositein association with temperature changes to be propagated and absorbedinto acicular crystals, thereby allowing this internal stress to beinhibited from being transmitted to the thermosetting resin. Thus,toughness of the thermosetting resin composite can be enhanced. Withthis, the light-reflective anisotropic conductive adhesive offersexcellent toughness, and can inhibit the occurrence of a crack andexfoliation of an adhesion surface even if the thermosetting resincomposite expands and contracts with temperature changes.

In a light-emitting device emitting visible light, the light-reflectiveacicular insulating particles are formed of an acicular inorganiccompound that appears white, reflecting light incident to thelight-reflective anisotropic conductive adhesive to the outside. Withthe light-reflective acicular insulating particles appearing white, wavelength dependency of reflection characteristics with respect to visiblelight can be decreased, and visible light can be efficiently reflected.

As such, with the light-reflective anisotropic conductive adhesive inthe present embodiment containing particles made of an acicularinorganic compound that appears white and has an aspect ratio within apredetermined ratio (these particles are hereinafter referred to as“white acicular inorganic particles”), a decrease in reflectance withrespect to light emitted from the light-emitting element is inhibited tomaintain luminous efficiency, and a crack and others are prevented toallow high conduction reliability to be obtained.

Examples of the white acicular inorganic particles can include zincoxide whiskers, titanium oxide whiskers, titanate whiskers such aspotassium titanate whiskers, aluminum borate whiskers, and needle-shapedinorganic compounds such as Wollastonite (needle crystal of kaolinsilicate). Whiskers are crystals growing in needle shapes with a specialprocess, and have advantages of high elasticity and resistance todeformation because of no irregularity in crystal structure. Theseinorganic compounds appear white in a light-emitting device emittingvisible light, and therefore have small wavelength dependency ofreflection characteristics with respect to visible light and tend toreflect visible light. Above all, zinc oxide whiskers are particularlypreferable because they have a high degree of whiteness and no catalyticproperty with respect to photodegradation even when there is a concernof photodegradation of a cured material of a curable resin composite ina cured anisotropic conductive adhesive.

When formed of crystals each having one acicular shape (single acicularcrystals), the white acicular inorganic particles preferably have afiber diameter (a short-direction diameter) equal to or smaller than 5μm. Also, the white acicular inorganic particles formed of singleacicular crystals preferably have an aspect ratio larger than 10 andsmaller than 35, and particularly preferably have an aspect ratio largerthan 10 and smaller than 20. When the aspect ratio of the white acicularinorganic particles is larger than 10, the internal stress of thethermosetting resin can be sufficiently propagated and absorbed. Also,when the aspect ratio of the white acicular inorganic particles issmaller than 35, the acicular crystals are less prone to be broken andcan be uniformly dispersed into the thermosetting resin, thereby notinhibiting anisotropic connection by the conductive particles. When thisaspect ratio is smaller than 20, dispersibility into the thermosettingresin can be further improved.

By adding white acicular inorganic particles having an aspect ratiolarger than 10 and smaller than 35 to the thermosetting resin composite,toughness of the thermosetting resin composite can be increased.Therefore, even if the light-reflective anisotropic conductive adhesiveexpands and contracts, exfoliation of the adhesion surface and theoccurrence of a crack can be inhibited.

Note that as the white acicular inorganic particles, in place of thesesingle acicular crystals, crystals each having a plurality of acicularshapes (plural acicular crystals) may be used, such as those each havinga shape of, for example, a Tetrapod®, in which a center part andvertexes of a tetrahedron are connected to each other. The whiteacicular inorganic particles of plural acicular crystals are excellentin large thermal conductivity compared with white acicular inorganicparticles of single acicular crystals, but have a bulky crystalstructure more than that of the single acicular crystals, and thereforeit is required to pay attention not to damage the substrate and bondingcomponents by an acicular portion at the time of thermocompression.

Also, the acicular white inorganic particles may be processed with, forexample, a silane coupling agent. With the acicular white inorganicparticles processed with the silane coupling agent, dispersibility inthe thermosetting resin composite can be improved. For this reason, theacicular white inorganic particles processed with the silane couplingagent can be uniformly mixed into the thermosetting resin composite fora short period of time.

The white acicular inorganic particles preferably have a refractiveindex (JIS K7142) preferably larger than the refractive index (JISK7142) of the cured matter of the thermosetting resin composite, andmore preferably larger by at least approximately 0.2. The reason forthis is that if the difference in refractive index is small, reflectionefficiency at an interface therebetween can be decreased. That is, eveninorganic particles are light-reflective and insulating, those such asSiO2 having a refractive index equal to or smaller than the refractiveindex of the thermosetting resin composite for use cannot be applied asthe white acicular inorganic particles.

When the content of the white acicular inorganic particles in thelight-reflective anisotropic conductive adhesive is too small,sufficient light reflection cannot be achieved. On the other hand, whenthe content is too large, adhesiveness of the thermosetting resin isdecreased. Therefore, the content is preferably 1 volume % (Vol %) to 50volume % with respect to the thermosetting resin composite, andparticularly preferably 5 volume % to 25 volume %.

The light-reflective anisotropic conductive adhesive in the presentembodiment contains these white acicular inorganic particles to coverthe most part of the conductive particles. Therefore, even if theconductive particles appear brown or the like, whiteness of thethermosetting resin composite can be achieved. With this whiteness ofthe thermosetting resin composite, wavelength dependency of reflectioncharacteristics with respect to visible light is decreased, and visiblelight can become easily reflective. Thus, irrespectively of the type ofcolor of the substrate electrodes, a decrease in reflectance of lightemitted from the LED element can be inhibited, and light emitted fromthe LED element toward its lower surface side can also be efficientlyutilized. As a result, luminous efficiency (light extraction efficiency)of the LED element can be improved.

And, in the light-reflective anisotropic conductive adhesive in thepresent embodiment, the shape of each of white inorganic particles asthe light-reflective insulating particles is acicular. With this, theinternal stress of the thermosetting resin composite with temperaturechanges can be propagated and absorbed into the acicular crystals toinhibit transmission of this internal stress to the thermosetting resin.Note that when the particle shape is globular, the internal stress ofthe thermosetting resin composite is less prone to be propagated andabsorbed into the particles, compared with the case of the acicularparticles.

As such, since the light-reflective anisotropic conductive adhesiveinhibits transmission of this internal stress to the thermosettingresin, toughness of the thermosetting resin composite can be enhanced.With this, the light-reflective anisotropic conductive adhesive offersexcellent toughness, and can inhibit the occurrence of a crack andexfoliation of the adhesion surface even if the thermosetting resincomposite expands and contracts with temperature changes.

Note that the light-reflective anisotropic conductive adhesive in thepresent embodiment may be formed by adding white acicular inorganicparticles to a thermosetting resin composite containing particles madeof a globular inorganic compound that appears white as light-reflectiveinsulating particles (these particles are hereinafter referred to as“white globular inorganic particles”). The white globular inorganicparticles are preferably made of a material similar to that of the whiteacicular inorganic particles described above, and those such as SiO2having a refractive index lower than the refractive index of thethermosetting resin composite for use cannot be applied.

With addition of the white globular inorganic particles together withthese white acicular inorganic particles, the thermosetting resincomposite can be further whitened to further improve light extractionefficiency of the LED element. Also in this case, toughness of thethermosetting resin can be enhanced. Here, the amount of addition (Vol%) of the white acicular inorganic particles is preferably equal to orlarger than the amount of addition (Vol %) of the white globularinorganic particles.

White globular inorganic particles tend to have low reflectance whenthey are too small and tend to inhibit connection by anisotropicconductive particles when they are too large. Therefore, their size ispreferably 0.02 μm to 20 μm, and more preferably 0.2 μm to 1 μm.

The white globular inorganic particles preferably have a refractiveindex (JIS K7142) larger than the refractive index (JIS K7142) of thecured matter of the thermosetting resin composite, and more preferablyhave a refractive index by at least 0.02.

As the globular light-reflective insulating particles, in place of thesewhite globular inorganic particles, resin-coated metal particles havinga surface of globular metal particles coated with a transparentinsulating resin may be used. As the metal articles, those made ofnickel, silver, aluminum, or the like can be cited.

As for the size of the resin-coated metal particles, a particle diameterof 0.1 μm to 30 μm is preferable, and 0.2 μm to 10 μm is morepreferable. Note that the size of the resin-coated metal particlesrepresents the size including the insulating coating.

As the resin in these resin-coated metal particles, various insulatingresins can be used. In view of functional strength and transparency, acured matter of an acryl-based resin can be preferably utilized.Preferably, a resin obtained by radical copolymerization of methylmethacrylate and methacrylate 2-hydroxyethyl under the presence of afree-radical initiator such as an organic peroxide such as benzoylperoxide can be cited. In this case, the resin is more preferablycross-linked with an isocyanate-based cross-linking agent such as2,4-tolylene diisocyanate.

Also, in metal particles, a y-glycidoxy group, a vinyl group, or thelike is preferably introduced in advance to a metal surface by using asilane coupling agent.

These resin-coated metal particles can be manufactured by, for example,introducing metal particles and a silane coupling agent into a solventsuch as toluene, agitating them for approximately one hour at a roomtemperature, and then introducing a radical monomer, a radicalpolymerization initiator, and, as required, a cross-linking agent andagitating them while heating to a radical polymerization starttemperature.

In the light-reflective anisotropic conductive adhesive, even when whiteglobular inorganic particles are added together with the white acicularinorganic particles, the light-reflective anisotropic conductiveadhesive can offer excellent toughness, thereby inhibiting exfoliationof the adhesion surface and the occurrence of a crack even withexpansion and contraction with temperature changes.

As the conductive particles contained in the light-reflectiveanisotropic conductive adhesive in the present embodiment, particles ofa metal material used in conventional conductive particles foranisotropic conductive connection can be used. That is, examples of themetal material of the conductive particles can include gold, nickel,copper, silver, soldering, palladium, aluminum, an alloy thereof, and amultilayered matter thereof (for example, nickel plating/metal flashplating matter).

Note that since the conductive particles with gold, nickel, or copperbeing taken as a metal material appear brown, the effects of the presentinvention can be enjoyed more than other metal materials. That is, asdescribed above, since white acicular inorganic particles covers themost part of the conductive particles in the thermosetting resincomposite, brownish appearance of the thermosetting resin composite dueto the conductive particles is inhibited, and the whole thermosettingresin composite comes to have a high degree of whiteness.

Also, as the conductive particles, metal-coated resin particles obtainedby coating resin particles with a metal material may be used. Examplesof these resin particles can include styrene-based resin particles,benzoguanamine resin particles, and nylon resin particles. As a methodof coating the resin particles with the metal material, a conventionallyknown method can be adopted. For example, an electroless plating method,an electroplating method, or others can be used. Also, the layerthickness of the coating metal material is any as long as goodconnection reliability can be ensured, normally 0.1 μm to 3 μm, althoughit depends on the particle diameter of the resin particles and the typeof the metal.

Also, a conduction defect tends to occur when the particle diameter ofthe resin particles is too small, and an inter-pattern short circuittends to occur when the particle diameter is too large. Therefore, theparticle diameter is preferably 1 μm to 20 μm, more preferably 3 μm to10 μm, and further particularly preferably 3 μm to 5 μm. In this case,each of the resin particles is preferably in a globular shape, but maybe in a flaky shape or a rugby-ball shape.

The metal-coated resin particles each have a globular shape, and itsparticle diameter is preferably 1 μm to 20 μm, and more preferably 3 μmto 10 μm, because connection reliability is decreased if the diameterparticle is too large.

Note that the conductive particles contained in the light-reflectiveanisotropic conductive adhesive in the present embodiment can belight-reflective conductive particles provided with light reflectiveproperties as depicted in, for example, FIG. 1A and FIG. 1B.

A light-reflective conductive particle 10 depicted in FIG. 1A isconfigured of a core particle 1 coated with a metal material and a lightreflective layer 3 on a surface thereof and formed from inorganicparticles 2 of at least one type selected from titanium oxide (TiO2)particles, zinc oxide (ZnO) particles, and aluminum oxide (Al2O3)particles. The light reflective layer 3 formed from these inorganicparticles appears a color in a range from white to gray. For thisreason, as described above, wavelength dependency of reflectioncharacteristics with respect to visible light is small, visible lightcan be easily reflected, and luminous efficiency of the LED element canbe more improved.

Note that when there is a concern of photodegradation of the curedmatter of the thermosetting resin composite of the cured anisotropicconductive adhesive, as described above, from among the titanium oxideparticles, the zinc oxide particles, and the aluminum oxide particles,the zinc oxide having no catalytic property with respect tophotodegradation and also having a high refractive index can bepreferably used.

The core particle 1 is for anisotropic conductive connection, and has asurface configured of a different metal material. Examples of the formof the core particle 1 can include a form in which the core particle 1itself is made of a metal material, or a form in which the surface ofthe resin particles is covered with a metal material.

In view of a relative size with respect to the particle diameter of thecore particle 1, when the layer thickness of the light reflective layer3 formed from the inorganic particles 2 is too small with respect to theparticle diameter of the core particle 1, a decrease in reflectancebecomes significant. When the layer thickness is too large, a conductiondefect occurs. For this reason, the layer thickness of the lightreflective layer 3 is preferably 5% to 50%, and more preferably 1% to25%.

Also, in light-reflective conductive particles 10, when the particlediameter of the inorganic particles 2 configuring the light reflectivelayer 3 is too small, a light reflecting phenomenon tends to be hard tooccur. When the particle diameter is too large, formation of the lightreflective layer tends to be difficult. For this reason, the particlediameter of the inorganic particles 2 is preferably 0.02 μM to 4 μm, andparticularly preferably 0.1 μm to 1 μm or 0.2 μm to 0.5 μm. In thiscase, in view of the wavelength of light for light reflection, theparticle diameter of the inorganic particles 2 is preferably equal to orlarger than 50% of the wavelength of light so that the light to bereflected (that is, light emitted from the light-emitting element) isprevented from passing. In this case, the inorganic particle 2 can havea formless shape, a globular shape, a scale shape, an acicular shape,and other shapes. Above all, the globular shape is preferable in view ofa light diffusion effect, and the scale shape is preferable in view of atotal reflection effect.

The light-reflective conductive particles 10 can be manufactured by aknown film forming technology (a so-called mechanofusion method) offorming a film of small particles on a surface oflarge-particle-diameter particles by causing physical collision amonglarge and small powders. In this case, the inorganic particles 2 arefixed so as to be engaged into the metal material on the surface of thecore particle 1. On the other hand, the inorganic particles are lessprone to be fused and fixed to each other. Thus, a mono-layer of theinorganic particles configures the light reflective layer 3. Therefore,in the case of FIG. 1A, the layer thickness of the light reflectivelayer 3 is considered to be equivalent to or slightly thinner than theparticle diameter of the inorganic particles 2.

Light-reflective conductive particles 20 depicted in FIG. 1B contain athermoplastic resin 4 for which the light reflective layer 3 functionsas an adhesive. With this thermoplastic resin 4, the inorganic particles2 are fixed to each other, and the inorganic particles 2 aremultilayered (for example, forming two layers or three layers), which isdifferent from the light-reflective conductive particles 10 of FIG. 1A.With this thermoplastic resin 4 being contained, mechanical strength ofthe light reflective layer 3 is improved, and exfoliation of theinorganic particles is less prone to occur.

As the thermoplastic resin 4, a halogen-free thermoplastic resin can bepreferably used with the intension of a low environmental load. Forexample, polyolefin such as polyethylene or polypropylene, polystyrene,or acrylic resin can be preferably used.

These light-reflective conductive particles 20 can be manufactured alsoby a mecha-fusion method. When the particle diameter of thethermoplastic resin 4 to be applied to the mecha-fusion method is toosmall, an adhesion function is decreased. When the particle diameter istoo large, the resin is less prone to be attached to the core particle.Therefore, the particle diameter is preferably 0.02 μm to 4 μm, and morepreferably 0.1 μm to 1 μm. Also, when the content of this thermoplasticresin 4 is too small, the adhesion function is decreased. When thecontent is too large, an aggregate of the particles is formed.Therefore, the content is preferably 0.2 mass parts to 500 mass partswith respect to 100 mass parts of the inorganic particles 2, and morepreferably 4 mass parts to 25 mass parts.

As the thermosetting resin contained in the light-reflective anisotropicconductive adhesive in the present embodiment, a colorless andtransparent resin is preferably used. This is not to decrease lightreflection efficiency of the light-reflective conductive particles inthe anisotropic conductive adhesive and furthermore to allow incidentlight to be reflected with its light color unchanged. Here, “colorlessand transparent” means that the cured matter of the anisotropicconductive adhesive has an optical path length of 1 cm and a lighttransmission (JIS K7105) of 80% or higher, preferably 90% or higher,with respect to visible light having a wavelength of 380 nm to 780 nm.

In the light-reflective anisotropic conductive adhesive, a content ofconductive particles such as light-reflective conductive particles withrespect to 100 mass parts of the thermosetting resin composite ispreferably 1 mass part to 100 mass parts and more preferably 10 massparts to 50 mass parts, because a conduction defect tends to occur whenthe content is too small and an inter-pattern short circuit tends tooccur when the content is too large.

With addition of white acicular inorganic particles to the thermosettingresin composite, the light-reflective anisotropic conductive adhesive inthe present embodiment has a value of reflectance (JIS K7105) higherthan 9%, with respect to light having a wavelength of 450 nm. Thereflection characteristics of the light-reflective anisotropicconductive adhesive in the present embodiment achieves a reflectance(JIS K7105) of 30% or higher with respect to light having a wavelengthof 450 nm, by appropriately adjusting various other factors, forexample, the reflection characteristics and content of thelight-reflective conductive particles and the content composition of thethermosetting resin composite. Normally, the reflectance tends toincrease when the content of the light-reflective conductive particleshaving excellent reflection characteristics is increased.

Also, the reflection characteristics of the light-reflective anisotropicconductive adhesive can be evaluated from a point of view of arefractive index. That is, this is because when the reflection of thecured matter is larger than the refractive index of the cured matter ofthe thermosetting resin composite from which the conductive particlesand the light-reflective insulating particles are excluded, the lightreflection amount is increased at an interface between thelight-reflective insulating particles and a cured matter of theirsurrounding thermosetting resin composite. Specifically, a differenceobtained by subtracting the refractive index (JIS K7142) of the curedmatter of the thermosetting resin composite from the refractive index(JIS K7142) of the light-reflective insulating particles is desired tobe preferably 0.02 or higher, and more preferably 0.2 or higher. Notethat the thermosetting resin composite having an epoxy resin as a maincomponent has a refractive index of approximately 1.5.

As the thermosetting resin composite, one used in a conventionalanisotropic conductive adhesive and anisotropic conductive film can beused. In general, this thermosetting resin composite is obtained byadding a curing agent to an insulating binder resin. As the insulatingbinder resin, an epoxy-based resin having an alicyclic epoxy compound, aheterocyclic epoxy compound, a hydrogen-added epoxy compound, or thelike as a main component is preferably cited.

As the alicyclic epoxy compound, one having two or more epoxy groups ina molecule is preferably cited. This may be in the form of liquid orsolid. Specific examples can include glycidyl hexahydro bisphenol A,3,4-epoxy cyclohexenyl methyl-3′, and 4-epoxy cyclohexene carboxylate.Above all, glycidyl hexahydro bisphenol A, 3,4-epoxy cyclohexenylmethyl-3′, or 4-epoxy cyclohexene carboxylate can be preferably usedbecause optical transparency suitable for mounting of an LED element canbe ensured for the cured material and any of these compound is excellentin quick curability.

As the heterocyclic epoxy compound, an epoxy compound having a triazinering can be cited. Particularly preferably,1,3,5-tris(2,3-epoxypropyl)-1,3,5-triazine-2,4,6-(1H, 3H, 5H)-trione canbe cited.

As the water-added epoxy compound, the above-described alicyclic epoxycompound or heterocyclic epoxy compound to which hydrogen is added, orany of other known hydrogen-added epoxy compounds can be used.

The alicyclic epoxy compound, the heterocyclic epoxy compound, and thehydrogenated epoxy compound may be used singly, or two or more typesthereof can be used together. Also, in addition to any of these epoxycompounds, another epoxy compound may be used together unless theeffects of the present invention are impaired. Examples include:glycidyl ether obtained by causing polyhydric phenol and epichlorohydrinto react with each other, the polyhydric phenol such as bisphenol A,bisphenol F, bisphenol S, tetramethyl bisphenol A, diarylbisphenol A,hydroquinone, catechol, resorcin, cresol, tetrabromobisphenol A,trihydroxy biphenyl, benzophenone, bisresorcinol, bisphenol hexafluoroacetone, tetramethyl bisphenol A, tetramethyl bisphenol F,tris(hydroxyphenyl)methane, bixylenol, phenol novolac, or cresolnovolac; poly glycidyl ether obtained by causing aliphatic polyalcoholand epichlorohydrin to react with each other, the aliphatic polyalcoholsuch as glycerol, neopentyl glycol, ethylene glycol, propylene glycol,hexylene glycol, polyethylene glycol, or polypropylene glycol; glycidylether ester obtained by causing hydroxy carboxylate, such as p-hydroxybenzoic acid or β-hydroxy naphthoic acid, and epichlorohydrin to reactwith each other; polyglycidyl ester obtained from polycarboxylic acidsuch as phthalic acid, methyl phthalic acid, isophthalic acid,terephthalic acid, tetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, endomethylene hexahydrophthalic acid,trimellitic acid, or polymerized fatty acid; glycidyl aminoglycidylether obtained from aminophenol or aminoalkylphenol; glycidylaminoglycidyl ester obtained from amino benzoic acid; glycidyl amineobtained from aniline, toluidine, tribromoaniline, xylylenediamine,diaminocyclohexane, bisaminomethylcyclohexane,4,4′-diaminodiphenylmethane, or 4,4′-diaminodiphenylsulfone; or knownepoxy resins such as epoxidized polyolefin.

As the curing agent can include an acid anhydride, an imidazolecompound, and cyanogen, or others can be cited. Above all, an acidanhydride that is less prone to discolor the cured material, inparticular, an alicyclic acid anhydride, can be preferably used.Specifically, a methylhexahydrophthalic acid anhydride or the like canbe preferably cited.

When an alicyclic epoxy compound and an alicyclic acid anhydride-basedcuring agent are used in the thermosetting resin composite, theiramounts of use have a tendency that the amount of an uncured epoxycompound becomes more as the amount of the alicyclic acidanhydride-based curing agent is too small and corrosion of the adherendmaterial is promoted under the influence of a superfluous curing agentwhen the amount of the curing agent is too large. Therefore, for 100mass parts of the alicyclic epoxy compound, the alicyclic acidanhydride-based curing agent is used at a ratio of preferably 80 massparts to 120 mass parts and more preferably 95 mass parts to 105 massparts.

The light-reflective anisotropic conductive adhesive in the presentembodiment can be manufactured by uniformly mixing the thermosettingresin composite, the conductive particles, and the white acicularinorganic particles, which are light-reflective insulating particles,together. Also, in the case of making a light-reflective anisotropicconductive film, the thermosetting resin composite, the conductiveparticles, and the white acicular inorganic particles, which arelight-reflective insulating particles, are mixed together in a dispersedmanner with a solvent such as toluene, a PET film subjected to anexfoliation process is coated with the resultant mixture so as to have adesired thickness, and is then dried at a temperature on the order ofapproximately 80 degrees Celsius.

Next, a light-emitting device formed by mounting a light-emittingelement on a wiring board using the light-reflective anisotropicconductive adhesive in the present embodiment is described withreference to FIG. 2. A light-emitting device 200 depicted in FIG. 2 is alight-emitting device in which a space between a connection terminal 22on a substrate 21 and connection bumps 26 formed on an n electrode 24and a p electrode 25 of an LED element 23 as a light-emitting element iscoated with the light-reflective anisotropic conductive adhesivedescribed above, thereby achieving flip-flop mount of the substrate 21and the LED element 23. Here, a cured matter 100 of the light-reflectiveanisotropic conductive adhesive is formed with light-reflectiveinsulating particles 10 being dispersed into a cured matter 11 of athermosetting resin composite. Note that, as required, a transparentmold resin may be used for sealing so as to cover the whole LED element23.

In the above-structured light-emitting device 200, among light beamsemitted from the LED element 23, a light beam emitted toward a substrate21 side is reflected from the light-reflective insulating particles 10in the cured matter 100 of the light-reflective anisotropic conductiveadhesive and is emitted from an upper surface of the LED element 23.Therefore, a decrease in luminous efficiency can be prevented.

The structures other than the light-reflective anisotropic conductiveadhesive in the light-emitting device 200 (such as the LED element 23,the bumps 26, the substrate 21, and the connection terminal 22) can besimilar to structures in a conventional light-emitting device. Also, thelight-emitting device 200 can be manufactured by using a conventionalanisotropic conductive connection technology except that thelight-reflective anisotropic conductive adhesive in the presentembodiment is used. Note that as the light-emitting element, in additionto the LED element 23, a known light-emitting element can be applied ina range of not impairing the effects of the present invention.

EXAMPLES

Specific examples of the present invention are described below. Notethat the scope of the present invention is not restricted to any of theexamples described below.

Example 1

(Fabrication of Anisotropic Conductive Adhesive)

White acicular inorganic particles and conductive particles each havinga surface of a globular resin plated with gold (a particle diameter of 5μm) were mixed into a thermosetting resin composite made of an epoxycuring-based adhesive (an adhesive binder having CE2021P-MeHHPA as amain component), thereby fabricating an anisotropic conductive adhesive.The amount of addition of the white acicular inorganic particles was12.0 volume % with respect to the thermosetting resin composite. As thewhite acicular inorganic particles, titanium dioxide (TiO2) whiskershaving a long-direction particle diameter of 1.7 μm and ashort-direction particle diameter of 0.13 μm (an aspect ratio of 13.1)were used. Also, the amount of addition of the conductive particles was10 mass % with respect to the thermosetting resin composite.

(Evaluation of Optical Reflectance)

A white board was coated with the fabricated anisotropic conductiveadhesive so that the coating has a thickness of 100 μM, and was cured bybeing heated at 200 degrees Celsius for one minute. As for the obtainedcured matter, a total reflectance (specular reflection and diffusereflection) with respect to light having a wavelength of 450 nm withbarium sulfate taken as being a standard was measured by using aspectrophotometer (UV3100 manufactured by Shimadzu Corporation).

(Fabrication of LED-Mount Sample)

On a glass epoxy substrate having wirings where copper wirings at a 100μm-pitch were plated with Ni/Au (5.0 μm thickness/0.3 μm thickness),gold (Au) bumps having a height of 15 μm were formed by using a bumpholder (FB700 manufactured by KAIJO Corporation). On this epoxysubstrate with gold bumps, blue LED (Vf=3.2 V (If=20 mA)) elements wereflip-chip-mounted by using a light-reflective anisotropic conductiveadhesive under conditions of 200 degrees Celsius, twenty seconds, and 1kg/chip, thereby obtaining a test-purpose LED module.

(Evaluation of Total Luminous Flux Amount)

As for the obtained test-purpose LED module, a total luminous fluxmeasurement system (integrating sphere type) (LE-2100 manufactured byOtsuka Electronics Co., Ltd.) was used to measure a total luminous fluxamount (measurement condition If=20 mA (constant current control)).

(Evaluation as to Conduction Reliability and Presence or Absence ofOccurrence of Crack)

Conduction reliability and the presence or absence of occurrence of acrack were evaluated with a thermal cycle test (TCT). The test-purposeLED module was put into a TCT, and (a) 1000 cycles each for thirtyminutes at −40 degrees Celsius←→thirty minutes at 100 degrees Celsiusand (b) 1000 cycles each for thirty minutes at −55 degreesCelsius←→thirty minutes at 125 degrees Celsius were performed. That is,(a) the module was exposed to atmospheres at −40 degrees Celsius and 100degrees Celsius each for thirty minutes, and 1000 thermal cycles eachwith the above process being taken as one cycle were performed. Also (b)the module was exposed to atmospheres at −55 degrees Celsius and 125degreed Celsius, and 1000 thermal cycle each with the above processbeing taken as one cycle were performed

For evaluation of conduction reliability, regarding the test-purpose LEDmodule extracted from the TCT after 1000 cycles of the TCT wereperformed, a Vf value at the time of If=20 mA was measured. When anincrease in the Vf value from an initial Vf value is within 5%,conduction reliability was determined as excellent, and marked as “◯”.when an increase in the Vf value from the initial Vf value is equal toor larger than 5%, conduction reliability was determined as notexcellent and marked as “x”.

For evaluation of the presence or absence of the occurrence of a crack,after 1000 cycles of the TCT were performed, the test-purpose LED moduleextracted from the TCT was observed from an upper surface of a blue LEDelement by a metallographical microscope, thereby observing the presenceor absence of the occurrence of a crack. The case in which theoccurrence of a crack was not observed in the light-reflectiveanisotropic conductive adhesive is marked as “◯”, and the case in whichthe occurrence of a crack was observed in the light-reflectiveanisotropic conductive adhesive is marked as “x”.

Example 2

As the white acicular inorganic particles, zinc oxide (ZnO) whiskers(pana-tetra WZ-05F1 manufactured by AMTEC CO., LTD.) having along-direction particle diameter of 50 μm and a short-direction particlediameter of 3 μm (an aspect ratio of 16.7) were used. Other than that, aprocess similar to that of Example 1 was performed.

Example 3

As the white acicular inorganic particles, potassium titanate whiskers(TISMO series manufactured by Otsuka Chemical Co., Ltd.) having along-direction particle diameter of 20 μm and a short-direction particlediameter of 0.6 μm (an aspect ratio of 33.3) were used. Other than that,a process similar to that of Example 1 was performed.

Example 4

As the white acicular inorganic particles, those with the surface ofzinc oxide (ZnO) whiskers (pana-tetra WZ-05F1 manufactured by AMTEC CO.,LTD.) having a long-direction particle diameter of 50 μm and ashort-direction particle diameter of 3 μm (an aspect ratio of 16.7)processed with a silane coupling agent were used. Other than that, aprocess similar to that of Example 1 was performed.

Example 5

As the white acicular inorganic particles, zinc oxide (ZnO) whiskers(pana-tetra WZ-05F1 manufactured by AMTEC CO., LTD.) having along-direction particle diameter of 50 μm, a short-direction particlediameter of 3 μm, and an aspect ratio of 16.7 were added to thethermosetting resin composite at a ratio of 9.0 volume %. Also, whiteglobular inorganic particles (I type manufactured by SAKAI CHEMICALINDUSTRY CO., LTD.) of zinc oxide (ZnO) having a particle diameter of0.6 μm (an aspect ratio of 1.0) were added to the thermosetting resincomposite at a ratio of 3.0 volume %. Other than that, a process similarto that of Example 1 was performed.

Comparative Example 1

No white acicular inorganic particles were contained in the anisotropicconductive adhesive. Other than that, a process similar to that ofExample 1 was performed.

Comparative Example 2

In place of the white acicular inorganic particles of Example 1, whiteglobular inorganic particles of titanium oxide of 0.9 μm (an aspectratio of 1.0) were added to the thermosetting resin composite at a ratioof 12.0 volume %. Other than that, a process similar to that of Example1 was performed.

Comparative Example 3

In place of the white acicular inorganic particles of Example 1, whiteglobular inorganic particles of zinc oxide of 0.6 μm (an aspect ratio of1.0) were added to the thermosetting resin composite at a ratio of 12.0volume %. Other than that, a process similar to that of Example 1 wasperformed.

Table 1 shows the results of Examples 1 to 5 and Comparative Examples 1to 3.

TABLE 1 COM- COM- COM- PAR- PAR- PAR- ATIVE ATIVE ATIVE EXAM- EXAM-EXAM- EXAMPLE EXAMPLE EXAMPLE EXAMPLE EXAMPLE PLE PLE PLE 1 2 3 4 5 1 23 WHITE TYPE TiO₂ ZnO POTAS- ZnO (SUR- ZnO/ZnO — TiO₂ ZnO ACICULAR SIUMFACE INORGANIC TITAN- SILANE PARTICLE ATE PRO- CESS) PARTICLE 1.7 50 2050  50/0.6 — 0.9 0.6 DIAMETER (LONG) (μm) PARTICLE 0.13 3 0.6 3   3/0.6— 0.9 0.6 DIAMETER (SHORT) (μm) ASPECT 13.1 16.7 33.3 16.7 16.7/1.0  —1.0 1.0 RATIO ADDITION 12.0 12.0 12.0 12.0 9/3 — 12.0 12.0 AMOUNT (Vol%) CONDUCTIVE PLATING Au Au Au Au Au Au Au Au PARTICLE TYPE PARTICLE 5 55 5 5 5 5 5 DIAMETER (m) OUTER COLOR WHITE WHITE WHITE WHITE WHITE BROWNWHITE WHITE APPEARANCE OF ADHESIVE REFLECTANCE 450 nm (%) 55 35 30 35 408 62 40 OPTICAL TOTAL INITIAL 350 300 250 300 350 200 330 350 CHARAC-LUMI- STAGE TERISTIC NOUS FLUX AMOUNT (mlm) OUTER CRACK TCT (−40 to ∘ ∘∘ ∘ ∘ ∘ ∘ ∘ APPEAR- 100° C.) ANCE −1000 cyc TCT (−55 to ∘ ∘ ∘ ∘ ∘ ∘ x x125° C.) −1000 cyc ELECTRIC CONDUC- INITIAL ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ CHARAC- TIONSTAGE TERISTIC RELI- TCT (−40 to ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ABILITY 100° C.) −1000cyc TCT (−55 to ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 125° C.) −1000 cyc

As can be seen from the results of Example 1 shown in Table 1, thereflectance of the cured matter of the light-reflective anisotropicconductive adhesive obtained by adding 12.0 volume % of TiO2 (titaniumdioxide) having an aspect ratio of 13.1 as white acicular inorganicparticles to the thermosetting resin composite was 55% with respect tothe wavelength of 450 nm. Also, the total luminous flux amount of theLED mount sample using this light-reflective anisotropic conductiveadhesive was 350 (mlm). The reflectance and efficiency of extractinglight from the LED were both slightly decreased compared withComparative Example 2 using globular TiO2 (white globular inorganicparticles). However, a crack did not occur after 1000 cycles of a TCT(−40 degrees Celsius to 100 degrees Celsius) and after 1000 cycles of aTCT (−55 degrees Celsius to 125 degrees Celsius), and crack resistancewas improved.

As can be seen from the results of Example 2, the reflectance of thecured matter of the light-reflective anisotropic conductive adhesiveobtained by adding 12.0 volume % of ZnO (zinc oxide) having an aspectratio of 16.7 as acicular white inorganic particles to the thermosettingresin composite was 35% with respect to the wavelength of 450 nm. Also,the total luminous flux amount of the LED mount sample using thislight-reflective anisotropic conductive adhesive was 300 (mlm). Thereflectance and efficiency of extracting light from the LED were bothslightly decreased compared with Comparative Example 3 using globularZnO (white globular inorganic particles). However, a crack did not occurafter 1000 cycles of the TCT (−40 degrees Celsius to 100 degreesCelsius) and after 1000 cycles of the TCT (−55 degrees Celsius to 125degrees Celsius), and crack resistance was improved.

As can be seen from the results of Example 3, the reflectance of thecured matter of the light-reflective anisotropic conductive adhesiveobtained by adding 12.0 volume % of potassium titanate having an aspectratio of 33.3 as white acicular inorganic particles to the thermosettingresin composite was 30% with respect to the wavelength of 450 nm. Also,the total luminous flux amount of the LED mount sample using thislight-reflective anisotropic conductive adhesive was 250 (mlm). Thereflectance and efficiency of extracting light from the blue LED wereboth slightly decreased compared with Comparative Example 3 usinggranular ZnO (white globular inorganic particles). However, a crack didnot occur after 1000 cycles of the TCT (−40 degrees Celsius to 100degrees Celsius) and after 1000 cycles of the TCT (−55 degrees Celsiusto 125 degrees Celsius), and crack resistance was improved.

As can be seen from the results of Example 4, the reflectance of thecured matter of the light-reflective anisotropic conductive adhesiveobtained by adding 12.0 volume % of ZnO having an aspect ratio of 16.7as white acicular inorganic particles to the thermosetting resincomposite was 35% with respect to the wavelength of 450 nm. Also, thetotal luminous flux amount of the LED mount sample using thislight-reflective anisotropic conductive adhesive was 300 (mlm). Thereflectance and efficiency of extracting light from the LED were bothslightly decreased compared with Comparative Example 3 using granularZnO (white globular inorganic particles). However, a crack did not occurafter 1000 cycles of the TCT (−40 degrees Celsius to 100 degreesCelsius) and after 1000 cycles of the TCT (−55 degrees Celsius to 125degrees Celsius), and crack resistance was improved.

As can be seen from the results of Example 5, the reflectance of thecured matter of the light-reflective anisotropic conductive adhesiveobtained by adding 9.0 volume % of zinc oxide (ZnO) having an aspectratio of 16.7 as white acicular inorganic particles to the thermosettingresin composite and adding 3.0 volume % of globular ZnO (white globularinorganic particles) to the thermosetting resin composite was 40% withrespect to the wavelength of 450 nm. Also, the total luminous fluxamount of the LED mount sample using this light-reflective anisotropicconductive adhesive was 250 (mlm). The reflectance and efficiency ofextracting light from the LED were both slightly decreased compared withComparative Example 3 using granular zinc oxide (ZnO) as white globularinorganic particles. However, a crack did not occur after 1000 cycles ofthe TCT (−40 degrees Celsius to 100 degrees Celsius) and after 1000cycles of the TCT (−55 degrees Celsius to 125 degrees Celsius), andcrack resistance was improved.

As can be seen from the results of Comparative Example 1, thereflectance of the cured matter of the anisotropic conductive adhesiveobtained by not adding acicular white inorganic particles but adding 10mass % of conductive particles to the thermosetting resin composite was8% with respect to the wavelength of 450 nm. The total luminous fluxamount of the LED mount sample using this anisotropic conductiveadhesive was 200 (mlm). Since light having a wavelength of 450 nmemitted from the blue LED were absorbed into gold (Au), the reflectancewith respect to this light was decreased, thereby decreasing luminousefficiency (light extraction efficiency) of the blue LED was decreased.A crack did not occur after 1000 cycles of the TCT (−40 degrees Celsiusto 100 degrees Celsius) and after 1000 cycles of the TCT (−55 degreesCelsius to 125 degrees Celsius).

As can be seen from the results of Comparative Example 2, thereflectance of the light-reflective anisotropic conductive adhesiveobtained by adding 12.0 volume % of white globular inorganic particlesof titanium dioxide (TiO2) to the thermosetting resin composite was 62%with respect to the wavelength of 450 nm. The total luminous flux amountof the LED mount sample using this light-reflective anisotropicconductive adhesive was 390 (mlm). However, while a crack did not occurafter 1000 cycles of the TCT (−40 degrees Celsius to 100 degreesCelsius), a crack occurred after 1000 cycles of the TCT (−55 degreesCelsius to 125 degrees Celsius).

As can be seen from the results of Comparative Example 3, thereflectance of the light-reflective anisotropic conductive adhesiveobtained by adding 12.0 volume % of white globular inorganic particlesof zinc oxide (ZnO) to the thermosetting resin composite was 40% withrespect to the wavelength of 450 nm. The total luminous flux amount ofthe LED mount sample using this light-reflective anisotropic conductiveadhesive was 350 (mlm). While a crack did not occur after 1000 cycles ofthe TCT (−40 degrees Celsius to 100 degrees Celsius), a crack occurredafter 1000 cycles of the TCT (−55 degrees Celsius to 125 degreesCelsius).

Note that it has been found that, after 1000 cycles of the TCT (−40degrees Celsius to 100 degrees Celsius) and after 1000 cycles of the TCT(−55 degrees Celsius to 125 degrees Celsius), the anisotropic conductiveadhesives of Examples 1 to 5 and Comparative Examples 1 to 3 initiallyhave high resistance to these temperature changes and offer excellentconduction reliability.

As can be seen from the results described above, in Examples 1 to 5using the light-reflective anisotropic conductive adhesive with whiteacicular inorganic particles added to the thermosetting resin composite,a decrease in reflectance with respect to light emitted from the LEDelement can be inhibited, and luminous efficiency (light extractionefficiency) of the LED element can be improved. Also, in thelight-reflective anisotropic conductive adhesives in Examples 1 to 5,high crack resistance was confirmed even after the TCT. The reason forthis can be thought such that toughness of the thermosetting resincomposite can be increased by the white acicular inorganic particlesformed of acicular shapes. Also, it was found that the light-reflectiveanisotropic conductive adhesives in Examples 1 to 5 have high resistanceto temperature changes and offer excellent conduction reliability.

REFERENCE SIGNS LIST

21 . . . substrate, 22 . . . connection terminal, 23 . . . LED element,24 . . . n electrode, 25 . . . p electrode, 26 . . . bump, 200 . . .light emitting device

1. A light-reflective anisotropic conductive adhesive to be used foranisotropic conductive connection of a light-emitting element to awiring board, the adhesive containing a thermosetting resin, conductiveparticles, and light-reflective acicular insulating particles.
 2. Thelight-reflective anisotropic conductive adhesive according to claim 1,wherein the light-reflective acicular insulating particles are inorganicparticles of at least one type selected from the group comprisingtitanium oxide, zinc oxide, and titanate.
 3. The light-reflectiveanisotropic conductive adhesive according to claim 1, wherein thelight-reflective acicular insulating particles are formed by processinga surface of zinc oxide with a silane agent.
 4. The light-reflectiveanisotropic conductive adhesive according to claim 1, wherein thelight-reflective acicular insulating particles have an aspect ratiolarger than 10 and smaller than
 35. 5. The light-reflective anisotropicconductive adhesive according to claim 1, wherein the light-reflectiveacicular insulating particles have an aspect ratio larger than 10 andsmaller than
 20. 6. The light-reflective anisotropic conductive adhesiveaccording to claim 1, wherein a content of the light-reflective acicularinsulating particles in the thermosetting resin composite is 1 volume %to 50 volume % with respect to the thermosetting resin composite.
 7. Thelight-reflective anisotropic conductive adhesive according to claim 1,wherein the adhesive further includes light-reflective globularinsulating particles.
 8. The light-reflective anisotropic conductiveadhesive according to claim 7, wherein the light-reflective acicularinsulating particles are contained with a volume amount equal to orlarger than a volume amount of the light-reflective globular insulatingparticles.
 9. A light-emitting device in which a light-emitting elementis mounted on a wiring board by a flip-chip method via thelight-reflective anisotropic conductive adhesive according to claim 1.10. The light-emitting device according to claim 9, wherein thelight-emitting element is a light-emitting diode.
 11. Thelight-reflective anisotropic conductive adhesive according to claim 2,wherein the light-reflective acicular insulating particles have anaspect ratio larger than 10 and smaller than
 35. 12. Thelight-reflective anisotropic conductive adhesive according to claim 3,wherein the light-reflective acicular insulating particles have anaspect ratio larger than 10 and smaller than
 35. 13. Thelight-reflective anisotropic conductive adhesive according to claim 2,wherein the light-reflective acicular insulating particles have anaspect ratio larger than 10 and smaller than
 20. 14. Thelight-reflective anisotropic conductive adhesive according to claim 3,wherein the light-reflective acicular insulating particles have anaspect ratio larger than 10 and smaller than
 20. 15. Thelight-reflective anisotropic conductive adhesive according to claim 2,wherein a content of the light-reflective acicular insulating particlesin the thermosetting resin composite is 1 volume % to 50 volume % withrespect to the thermosetting resin composite.
 16. The light-reflectiveanisotropic conductive adhesive according to claim 3, wherein a contentof the light-reflective acicular insulating particles in thethermosetting resin composite is 1 volume % to 50 volume % with respectto the thermosetting resin composite.
 17. The light-reflectiveanisotropic conductive adhesive according to claim 4, wherein a contentof the light-reflective acicular insulating particles in thethermosetting resin composite is 1 volume % to 50 volume % with respectto the thermosetting resin composite.
 18. The light-reflectiveanisotropic conductive adhesive according to claim 5, wherein a contentof the light-reflective acicular insulating particles in thethermosetting resin composite is 1 volume % to 50 volume % with respectto the thermosetting resin composite.